Conventionally, there is known an art of cooling an exhaust system of an internal combustion engine (more particularly, an exhaust manifold, for example) by a refrigerant such as water. As to such an art, an art that may be relative to the present invention is disclosed in Patent Document 1. In Patent Document 1, there is disclosed an exhaust manifold apparatus equipped with a water jacket formed around an exhaust manifold and a water injection means that injects water to the water jacket in the form of spray.    Patent Document 1: Japanese Patent Application Publication No. 63-208607